1. Field
This document relates to a data modulation method and a liquid crystal display using the same.
2. Related Art
Image display devices are classified into a stereoscopic technique and an autostereoscopic technique. The stereoscopic technique uses binocular parallax images which are great in the stereoscopic effect, and may have a type of using glasses and a type of not using glasses. In the type of using glasses (“glass type”), binocular parallax images are displayed on a direct view display panel or a projector by changing polarization directions or in the temporal division manner, and polarization glasses or liquid crystal shutter glasses are used to implement stereoscopic images. In the type of not using glasses (“glassless type”), the stereoscopic images are implemented by dividing optical axes of binocular parallax images, by using optical plates such as parallax barriers provided at front and rear surfaces of a display panel.
The glass type stereoscopic image display device typically displays left eye images and right eye images on a display panel in a temporal division manner. The glasses worn by a user is constituted by a left eye filter (or a left eye shutter) which transmits light for left eye images and a right eye filter (or a right eye shutter) which transmits light for right eye images. Thus, the user sees only the left eye images, for example, during odd frames, and sees only the right eye image during even frames, thereby obtaining a three-dimensional effect by a binocular parallax.
In a liquid crystal display to implement stereoscopic images, liquid crystal of the liquid crystal display is slow in a response speed due to characteristics such as unique viscosity and elasticity.
                              τ          r                ∝                              γ            ⁢                                                  ⁢                          d              2                                            Δɛ            ⁢                                                                          V                  a                  2                                -                                  V                  F                  2                                                                                                      (        1        )            
In Equation (1), τr indicates a rising time when a voltage is applied to the liquid crystal, Va indicates an applied voltage, VF indicates Freederick transition voltage when the liquid crystal molecules starts a tilted motion, d indicates a cell gap of a liquid crystal cell, and γ indicates a rotational viscosity of the liquid crystal molecules.
                              τ          f                ∝                              γ            ⁢                                                  ⁢                          d              2                                K                                    (        2        )            
In Equation (2), τf indicates a falling time when the liquid crystal is recovered to an original position due to the elastic recovery after the liquid crystal stops being applied with a voltage, and K indicates a modulus of elasticity unique to the liquid crystal.
In the liquid crystal display, as a method for improving the response speed of the liquid crystal, there is known an overdriving method. The over-driving method modulates a data value for a current frame to a higher value if a data value of an input image in the current frame becomes larger than that in a previous frame, whereas it modulates a data value for a current frame to a lower value if a data value of the input image in the current frame becomes smaller than that in a previous frame, thereby adjusting data voltages applied to liquid crystal cells to compensate a slow response characteristic of the liquid crystal. The over-driving method may be implemented by a look-up table where the data values for previous and current frames of an input image are input and corresponding pre-stored modulation values are output. However, when an overdriving method for 2D images is applied to 3D images, the overdriving method has a problem in that a brightness difference is generated depending on a grayscale for a previous frame data in representing the same grayscale in 3D image data. Further, a 3D crosstalk occurs in which left eye images and right eye images overlap each other due to the brightness difference.